So, what exactly is 4D printing?
Additive manufacturing (or 3D printing) is 30 years-old this year. Today, it’s found not just in industries but also in households, as the price of 3D printers has fallen below Dhs3,500. Knowing you can print almost anything opens up unlimited opportunities for us to manufacture toys, household appliances and tools in our living rooms.
But there’s more that can be done with 3D-printed materials to make them more flexible and more useful: structures that can transform in a pre-programmed way in response to a stimulus. Recently given the popular-science name of “4D printing”, perhaps a better way to think about it is that the object transforms over time.
These sorts of structural deformations are not new. Researchers have already demonstrated “memory” and “smart material” properties. One of the most popular technologies is known as shape-memory alloy, where a change of temperature triggers a shape change. Other successful approaches use electroactive polymers, pressurised fluids or gasses, chemical stimuli and even response to light.
In a paper published in Nature’s Scientific Reports, researchers at MIT looked at the design of complex self-deformations in objects that have been printed from multiple materials to customise the object into specific forms.
Unlike many others who have demonstrated how to bend simple paper-like shapes, the researchers constructed a two-dimensional grid structure that deforms itself by stretching or shrinking across a complex three-dimensional surface.
Imagine dropping a flat stretchable cloth onto a randomly shaped object, where the cloth moulds over the shape beneath it. In geometrical terms, as the curvature of the cloth changes to fit the object, the distances and areas alter. This was taken into account by providing a solution that copes with bending and also expansion in size. Several designs were formulated that demonstrated that this is possible.
Head of the MIT’s Self-Assembly Laboratory, Skylar Tibbits, started this line of research a few years ago with expanding materials and simple deformations. The collaboration of researchers from MIT’s Camera Culture group and Self-Assembly Laboratory and the companies Stratasys and Autodesk Inc took this further.
The approach used was to print 3D structures using materials with different properties: one that remained rigid and another that expanded by up to 200 percent of its original volume. The expanding materials were placed strategically on the main structure to produce joints that stretched and folded like a bendy straw when activated by water, forming a broad range of shapes. For example, a 3D-printed shape that resembled the initials “MIT” was shown to evolve into another formation that looks like the initials “SAL”.
It’s easy to imagine a wide range of applications such as home appliances and products that can adapt to heat or moisture to improve comfort or add functionality. Childcare products that can react to humidity or temperature, for example, or clothes and footwear that optimise their form and function by reacting to changes in the environment.
There are many more uses these could be applied to if they can be manufactured to change shape and function without external intervention from a surgeon. Individually designed cardiac tubes are one good example.
This was a proof of concept for self-transforming materials, with an easy production process and an available suite of tools to customise and analyse the process.
But even so, this is just scratching the surface.
A future aim for researchers is to produce larger structures that can handle more complex transformations, as well as smaller, miniaturised models that can be used in the body. While deformations were found that could be applied and reversed repeatedly, the material degraded after a while, so long-term durability needs improving.
With 4D printing there’s a lot to play with. Now, that 3D printing has captured our imagination, just think what adding time to the equation could do.
And should you want a technical (quite cool looking) video of how it works, see below…